Shan X, Davis J H, Chu J W, Sharom F J
Department of Physics, University of Guelph, Ont., Canada.
Biochim Biophys Acta. 1994 Jul 13;1193(1):127-37. doi: 10.1016/0005-2736(94)90341-7.
Deuterium nuclear magnetic resonance spectroscopy was used to investigate the phase equilibria, and the temperature and concentration dependences of the phospholipid hydrocarbon chain order, of mixtures of glycophorin in dimyristoylphosphatidyl-choline. In the fluid phase it is found that the protein has only a slight effect on the first moment of the 2H spectrum, which for perdeuterated chains is a direct measure of the average chain orientational order. However, analysis of the rate of change of the first moment with respect to protein concentration, at different temperatures within the fluid phase, shows that at a molar protein concentration of about 0.0295 +/- 0.01, the lipid chain order (or M1) is essentially independent of temperature. At this concentration the chain order is determined by the lipid's interaction with the protein and one can conclude that about 34 (+/- 12) lipids are required to solvate the protein. At higher lipid concentrations these lipids are freely exchanging, on the NMR time scale, with the other lipids in the bilayer. At glycophorin concentrations below about 1 mol% there is a two-phase coexistence region at temperatures below the pure lipid's chain melting transition. The boundary between the fluid phase and this two-phase region curves downwards (is concave downwards), whereas the boundary between the two-phase region and the gel phase, while naturally occurring at lower temperatures than the upper boundary, is concave upwards. As a consequence the protein partitions preferentially into the fluid phase. This behaviour is similar to that observed in a number of other protein/lipid and peptide/lipid mixtures where it was suggested that those systems may have been close to a critical mixing point and some characteristics of a continuous phase change were noted. Indeed, at glycophorin concentrations near and above 1 mol% there are indications that the phase behaviour becomes more complex, suggesting the presence of significant protein/protein interactions and that this system may be close to a critical point.
利用氘核磁共振光谱研究了糖蛋白与二肉豆蔻酰磷脂酰胆碱混合物的相平衡，以及磷脂烃链有序性的温度和浓度依赖性。在流体相中发现，该蛋白质对2H谱的一阶矩只有轻微影响，对于全氘化链来说，这是平均链取向有序性的直接度量。然而，分析流体相内不同温度下一阶矩相对于蛋白质浓度的变化率表明，在摩尔蛋白质浓度约为0.0295±0.01时，脂质链有序性（或M1）基本与温度无关。在此浓度下，链有序性由脂质与蛋白质的相互作用决定，可以得出结论，约34（±12）个脂质分子需要用于溶解该蛋白质。在较高脂质浓度下，这些脂质分子在核磁共振时间尺度上与双层中的其他脂质分子自由交换。在糖蛋白浓度低于约1 mol%时，在低于纯脂质链熔化转变温度的条件下存在一个两相共存区域。流体相与该两相区域之间的边界向下弯曲（向下凹），而两相区域与凝胶相之间的边界虽然自然出现在比上边界更低的温度下，但却是向上凹的。因此，蛋白质优先分配到流体相中。这种行为类似于在许多其他蛋白质/脂质和肽/脂质混合物中观察到的行为，在这些混合物中有人认为那些系统可能接近临界混合点，并注意到了连续相变的一些特征。实际上，在糖蛋白浓度接近和高于1 mol%时，有迹象表明相行为变得更加复杂，这表明存在显著的蛋白质/蛋白质相互作用，并且该系统可能接近临界点。
